Population Genetic Structure and Population History of the Biting Midge Culicoides mahasarakhamense (Diptera: Ceratopogonidae)

Simple Summary Biting midges are important blood sucking insects. Many species are pests of humans and other animals, including economically important livestock. A new biting midge species, Culicoides mahasarakhamense, was recently described in Thailand. This species is a pest and a potential vector of blood protozoa transmitted to domestic chickens and other avian species. Knowledge of genetic diversity and genetic differentiation among populations of vector species is of paramount importance as it can be used to design effective control programs. However, this information is lacking for C. mahasarakhamense. In this study, we used mitochondrial cytochrome c oxidase I (COI) sequences as genetic markers to evaluate the level of genetic diversity and the genetic structure of C. mahasarakhamense from Thailand. The level of genetic diversity was relatively high, but most populations were not genetically different. However, one population from northern Thailand was found to be genetically highly different from others. Historical population isolation and geographic distance separation are possible explanations for the high level of genetic differentiation. This information will help in monitoring the spread of the parasitic disease agents carried by C. mahasarakhamense from different populations. Biting midges of the genus Culicoides Latreille are significant pests and vectors of disease agents transmitted to humans and other animals. Understanding the genetic structure and diversity of these insects is crucial for effective control programs. This study examined the genetic diversity, genetic structure, and demographic history of Culicoides mahasarakhamense, a possible vector of avian haemosporidian parasites and Leishmania martiniquensis, in Thailand. The star-like shape of the median joining haplotype network, a unimodal mismatch distribution, and significant negative values for Tajima's D and Fu's F-S tests indicated that populations had undergone recent expansion. Population expansion time was estimated to be 2000-22,000 years ago. Population expansion may have been triggered by climatic amelioration from cold/dry to warm/humid conditions at the end of the last glaciations, resulting in the increased availability of host blood sources. Population pairwise F-ST revealed that most (87%) comparisons were not genetically different, most likely due to a shared recent history. The exception to the generally low level of genetic structuring is a population from the northern region that is genetically highly different from others. Population isolation in the past and the limitation of ongoing gene flows due to large geographic distance separation are possible explanations for genetic differentiation.